This invention relates generally to contact lenses and more particularly to the fabrication of contact lenses.
Defects in human vision have for years been corrected by placing lenses, commonly referred to as glasses, of a prscribed design in front of the eye. Recently, as an alternative to glasses, contact lenses were developed. Contact lenses are thin lenses, typically made of a plastic material, fitted over the cornea to correct vision defects. A process for fabricating contact lenses involves filling a plastic casting mold with contact lens material in liquid monomer form. The liquid is then polymerized into a solid. The casting mold is precision manufactured such that the contact lens formed in the mold is of a prescribed edge dimension and the concave surface is of a prescribed finished optical design and quality. Once the convex surface of the lens is cut and polished to the prescribed optical quality, the lens can beremoved from the casting mold and is in a completely finished state.
while the above process has enabled contact lenses to be produced in mass quantities with high optical quality, the effective yield (i.e., the number of good lenses per total number of molded lenses) is low. This low yield is primarily due to the fact that removal of a lens from the plastic casting mold has been difficult. Such removal involves either floating the lens off of the casting mold in a liquid bath or deforming the casting mold such as by squeezing the mold with pliers for example. The liquid bath is an inefficient process only cost justified for large batches of lenses. Moreover, it is only effective for lenses made with liquid permiable material. On the other hand, deforming of the casting mold is a manual process, usable on only one mold at a time, requiring a high degree of skill to prevent braking of the lens as the mold is deformed.